High-temperature bimetal thermostat



July 7, 1953 Filed March 5 1951 N. MILL-ER HIGH-TEMPERATURE BIMETALTHERMSTAT- 4 Sheets-Sheet l July 7, 1953 N. MILLER HIGH-TEMPERATUREBIME'IAL. THERMOSTAT Filed March 3, 195i July 7, 1953 N. MILLER2,644,874

HIGH-TEMPERATURE IMETAL THERMOSTAT.

Filed March 3, 1951 4 Sheath-Sheet 3 #www in: I/Hnl NM S July 7, 1953 N.MILLER 2,644,874.

HIGH-TEMPERATURE lBIMETAL THERMOSTAT Filed March s, 1951' 4 sheets-sheet4,

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I 7/ 42 3 iwf/3 cs 55 m 56 5? .fm/enzzo" Patented July 7, l1953 UNITEDs1-Ares PATENT ole-FICE `AHIGH-TEMI'IIERA'IU'RE BIMETAL THERMOSTAT fNicholas `MillerBerwyn,fIll., assignor to General .Electric Company, acorporation of New York Application March 3, 1951, Serial No. 213,740

11 Claims.y (Cl. 20D- 138) This invention relates vto temperaturevresponsive control devices, :and yin particular, to: a thermostat ofthe vbimetal 'type adapted kfor the control of .temperatures ranging `upto 1000 degrees F.

Insofa-ras I am "aware, no .bimetal thermostat has heretofore beencapable of satisfactorily controlling temperatures 'above '700 degrees:F.,

ffor various reasons. Bimetalsl capabler of withstats are self-containeddevices in which the .en-

tire structure may be exposedto substantiallythe temperature of theldevice being controlled. As

va result, their component parts are subject to operating temperatures`and other conditions much more severefthan oonventionalliquid or thermalexpansion thermostats in which the casing housing theadjustment-devices,y 'contacts-"and other rather -vulnerableelementsf isnot subject to extremely high temperatures. yIn a bimetal Vthermostat`small differences in Jco-eiiieients Vof thermal expansion of pivotally`associated .parts may result in a hindi-rigor rabnormally stiffmovement of such parts, and means must'be provided for maintaining freemovement of such parts at high temperatures while -avoidin'g'sloppinessand resulting loss 'of accuracy at substantially Ylower temperatures.

It is therefore aV principal object V`of my 'invention to provide vabimetal typethermostat which will provide temperature control yaccurateWithin commercial limits vover a range of 'from 250l degrees F. to 1000ydegrees F.

It is another object of `-myinvention to provide means for maintainingthe various `pivotall-y associated elements of the `thermostat in properoperative relationship throughout v'the operating temperature rangeofthe device.

It isa further object of my invention to provide a bimetal thermostatinwhich the relatively low sensitivity of high temperature-responsivebimetals may be `adapted to produce lowamplitude make-and-break action'oi theswitch contacts respect tothe bimetal element to establish .the fdesired operating temperature, said yoke being biased toward oneoperating condition by spring means having such operative relation tothe rigidity of the bimetal elementat high temperaturethat the bimetalelement will not be over- `stressed under operating conditions in whichthe spring bias may be transmitted through the yoke to the bimetal.

A further object of my invention is to provide an Aimproved flexibleconductor system between thethermostat contact means and-binding postsor terminals through which the thermostat is connected into the heatingelement control circuit.

`In a presently preferred embodiment of my invention adapted for thetemperature control of velectrically heated cook stoves and the like, I

secure a bimetal blade to a xed frame member of which a portion is indirect heat exchange relation contact with the cooking surface of thestove. 4A pair of contact elements is carried on an vextension of the'bimetal blade in insulated relation therewith. The end of the extensionis knife-edged. I pivotally attach to said frame a rigid yoke havingiixed contacts disposed in cooperative arrangement with respect to thecontacts on the bimetal member. By placingthe bimetal contact structureas near as possible to the'knife-fedge end of the bimetal extension, and

.utilizing an S-shaped throw spring between the knife edge and a springpivot point on the end of.ithe yoke, I amable to attain the desiredspeed.and extent of Ycontact separation even with the low order of responseof high-temperature bimetal. YAn adjusting screw directed against anYangularly extendingportion `of the yoke provides means .for rotatingthe yoke relative to the bi- `pressure exerted on the end oftheadjustment screw maintains the respective threaded elements inproperengagement to insure repetitive action of thespring regardless of thetemperature to whichthe screw is exposed.

VThe conductors between the contacts and the binding posts to Whichtheleads from the electrical controls-ystem areattached, arehighlyflexviblei; in a commercial application of my invention,

I employ thin Ystrips offsilver. These strips are supportedintermediatetheir ends Vby aiioating insulator'which permits'free flexing of thestrips `without strain onthecontact elements' vcarried by the movableyoke. rI'his is particularly advantageous when the thermostat isdirectly in the control circuit of a high Wattage heating system inwhich the circuit connections must be of relatively heavy, stiff, wire.It may be mentioned in passing that a thermostat embodying my inventionmay be used with any heating means capable of electrical control, suchas oil, gas, or automatic coal-stoking devices, and is therefore notrestricted to electric heating as such.

Means are provided to support the bimetal elcnient against flexing attemperatures below a predetermined minimum. For example, it may beconsiderd that the lowest operating temperature for a range thermostatmay be of the order of 250 degrees F. By providing a positive stop whichthe bimetal element will engage should the temperature dropsubstantially below that point, and by arranging the adjustment screwand yoke so that the yoke may be rotated to move its fixed contactssafely away from the contacts carried by the bimetal element, arelationship may convenientiy be attained in which regardless of howcool the birnetal becomes, the respective contact devices will not corneinto circuit-closing relationship. rl`he temperature-adjustrnent knobmaysuitably be marked with an olif position which will represent suchpermanently open state.

Other features and advantages of the invention will be apparent from thefollowing detailed description of a presently preferred embodiment readin connection with the accompanying drawings in which Fig. 1 is afragmentary side sectional elevation of a restaurant type electric rangeutilizing a thermostat embodying the present invention; Fig. 2 is afragmentary front elevation of the range and thermostat, the cookingsurface of the range being in section to show typical electric .heatingelements therein; Fig. 3 is a top plan viewof the thermostat; Fig. 4 isa side elevation thereof in section on the line 4--4 of Fig. 3, thethermostat being in the off position represented in Fig. 2; Fig. 5 is aside sectional elevation of the thermostat in closed circuit position; Grepresents the thermostat in open circuit position; '.7 is an endelevation in section along line l--l of Fig. 4; Fig. 8 is an oppositeend elevation; Fig. 9 is a partial side elevation with a wall of theyoke member broken away to show the limiting arm and indicating a methodof adjusting said arm; and Fig. 10 is an elevational section looking inthe direction of line lil- Ill of Fig. 3.

Although my thermostat is not restricted to such apparatus, it has beenillustrated in assou ciation with anelectric range of the restauranttype in which (see Fig. 1 and Fig. 2) a frame l is provided with acooking surface 2 having embedded therein a suitable plurality ofheating elements 3 which are preferably of the familiar sheathedresistance type having an outer metallic sheath within which iscontained an electric resistance element embedded in a densely compactedmass of granular material having electrically-insulating andheat-conducting properties. Such heating elements of the type are shownin the C. C. Abbott Patent #1,367,341 dated February 1, 1921. It is ofcourse understood that the heating elements are of relatively highwattage and are served by a suitable electrical circuit (not shown) aswell known to those skilledin the art. Rigidly screwed or otherwisesecured to a boss 4, extending downwardly from the cenward wall i3.

.of the associated channelv brackets.

.4 stat T embodying the present invention; a temperature-adjustment knob5 is suitably mounted on a front panel 5 or the range and is operativelyassociated with the thermostat-adjusting means by a shaft "i and, wherenecessary, a universal joint coupling E. A reflector plate il is usuallyplaced below the cooking top to reflect back the heat radiatingfromthe'c'ooking top, thus keeping the space within the range body fromrising to excessive temperatures. The temperature-adjustment knob 5 isgraduated to indicate thermo-- stat setting points in hundreds ofdegrees; the illustrated knob has graduations indicating a control rangeof from 390 to over 90@ degrees F. and also has an Uofi" indicator atwhich the thermostat will remain in open-circuit position regard less ofambient temperature, as later explained. lt should be noted that theknob `5 is rotated in clockwise direction to increase the settingtemperature, there being an index mark E on the front panel., as isconventional.

Referring nowv to Figs. 3 and fi, the thermostat T includes a rigidframe structure lll having a flat-ground top Wall li, side walls l2, aforaid forward wall is skeletal to provide an opening aboveatransversely entending bottom portionlil. Holes l5 may be provided intop wall i l to accommodate the screws (Fig. l) with which thethermostat is secured to the boss i for heat exchange relationship withcooking surface 2. A ceramic terminalblock i6 may be secured toforward'wall i3 by machine screws or equivalent Il'.

A composite bimetal element includes a first bimetal strip i8, one endof which is securely Ilxed to Wall Il by countersunk rivets I9, and asecond bimeta'l strip '20 riveted to the free end of strip it. It willbe noted that the larger portieri of strip 2t is stifened againstiiexure by the side wall flanges E l, thus restricting the fleXure ofthe strip to the flat area adjacent strip i8. For rea-- sons well. knownto those .skilled in the art, the respective strips I8 and ill arearranged so that they have an opposite response to temperature change.That is, where strip i3 ilexes downwardly of Fig. 3 upon decrease intemperature, strip 2i) fleiaes upwardly, and vice versa. Each or thesaid strips I8 and 2i] is preferably of a bimetal material made of highchromium alloy compoinents which withstand stresses at high temperatureswithout taking a permanent set. The biinetal manufactured by the W..ll/l. Chase Company ofr Detroit, Mich., and known as their ##4000bimetal, has been found satisfactory for control temperatures up to 1000degrees F.y

As has been previously noted, high temperature bimetals of the typementioned have a very low order of amplitude of movement for'teliperature change, and I therefore arrange the contact structure asclose as is practicabler to the end of the bimetal strip. Pursuant toknown practices, I arrange the contact assembly for a rather free swivelaction. For example, I suspend a light metal crossp-iece 2.2 from thestrip 2i) by means of a large-headed rivet 23 which passes through alarge diameter opening 2li in said strip. The rivet head rests upon arib 25 formed in said strip. symmetrically arranged relative to rib 25,are the inverted channel brackets 26, 2l, therespective side walls ofwhich are pierced (see ligs. 5 and 6) to receive the contact plates 2t,29, which are formed intermediate their ends with ears 28a, 29a, whichextend through the side wall openings As clearly tral area of thecooking surface 2, is a thermoappears in Fig. 6, :the side wall openingsof the ,as-44pm channel brackets provide for a fairly free 'rockingaction of the contact plates. The channel brackets are insulatedlysecured to the crosspiece by rivets 36 in association with 'the mica orother high-temperature resistant insulator Asheets 3 l, 32. The entirebimetal element contact assembly,

hereinafter identied by'33, is lheld against rotation in theplaneofstripZU by a tongu'e'34 extending from crosspiece 422 and passingwith moderate clearance through an-opening provided in said strip (seeFig. 3)

Adjustment or preselection of the temperature at which the thermostat isto exercise control is accomplished `by establishing a predeterminedrelationship between Contact assembly '33 and a set of iixed contacts 35Von a yoke member 36 pivotally supported on frame I0 and arranged Ato berotated relative thereto, as-later described. Said yoke may be a unitarystructure having side members 31, 38, rising from a bottom 39. Rivets 40may be used to pivotally .ax the yoke sides to the side wall-s of frameID. The ends 4l, 42, of the yoke side members overlap to provide a rigidwall on which to mount a :pivot screw 43 for the S-shaped overthrowspring 44, the opposite end of said spring being formed (see Fig. 4) toreceive the knife-edge end 45 of bimetal strip 2.6. l The side walls ofthe yoke 3'6 have a ratherfree pivotal play in their relationshipwiththe frame member Il! so as to minimize the lpossibility of bindingat elevated temperatures. As willlater appear, the temperatureadjustment means is so designed that more than usual freedom of play .ofthe respective pivotally mounted members may be utilized withoutdetriment to the accuracy or arrangement ci the thermostat. The yoke endportions are preferably welded together and adjustably carry a mountingplate 46 for the spring pivot screw 43, said screw passing through anenlargedv opening 4i in the yoke end walls. As best appears in Fig. 8,the pivot screwmou-nting plate 46 has an arcuate slot 48 which permitsrotational adjustment in the-plane of the ends of the yoke. The screws48, 50, are respectively for pivotally mounting the plate 46 and forholding the same in adjusted position. It should be noted in passingthat the end of the yoke is parallel to the axis of rotation-of the yokeabout Vits pivots, and is at right angles to the longitudinal axis ofthe bimetal system. The tip of screw 43 will be within acceptabletolerances in the vertical plane of said longitudinal axis throughoutthe range of adjustment of the support plate. Fixed contact assembly 35comprises pairs ofsilverfaced contacts 5I, 5m, and .52, 52a,respectively cooperating with the contact plates 28 and 2S in a doublepole, single throw, switch arrangement. The contacts are riveted to arelatively heavy body 53 of mica, or the like, which isiny turnrivetedor otherwisesecured to the face of the yoke. Pairs oi" terminal posts54, 54a,v and55, 55a, are provided in polygonal apertures in theterminal block i6, and are connected with the respective contact pairsby fiexible conductor strips 56, 56a, and 51, 51o.

wide have ample electrical capacity and are sufficiently iiexible topermit movement of-the 'yoke as presently described. The conductorstrips lare maintained in spaced insulated relationship by passagebetween the various arm members of an insulator 53 which is arranged forfloating movement in suitable slots v5i! provided in the terminal blockI6. This arrangement is clearly apparent in Figs. 5 and 8. Thiszelectricalfcon- I have found that strips of silver i 0.610 inch thickand approximately 3Ayofan inch the thermostat into the load circuit.

'the yoke.

`and Side walls of the yoke.

nection system is of appreciable importance in the present inventionwhere the load to be 'controlled is of 'such high wattage as to requireheavy lead wires 60, 66a and 6I, Gla, for vconnection fof It should benoted that the terminal posts themselves are relativelyloosely mountedin the `ceramic 'insulater i6, having both vertical and lateralclearancewith the walls thereof, asappears inFig. 4. The clearance permitsexpansionof. the terminal `posts up to the extreme high temperature ofcontrol without imposing strainson the yceramic insulator block. Toprevent rotation of the terminal posts within the apertures, the cross.sec-

`tion of the posts is similar toxthat of the apertures.

Ailixedto the floor of the vyoke is a bell 'crank member 62 having a leg63'extending downwardly from the yoke to position its end remote'fromtheG4-and the portion of the legimmediately above the extremity engaged bythe temperature adjustment screw is formed with a rib which merges intothe relatively high dome 65, rising from` the center'of the upper legportion 66, which in .turn has side wall iianges 61 vengaging the sideWallsof The .bell crank leg portion 66 is preferably spot welded atseveral points to the floor Dome 65 provides a seat for the end of atorsion spring 68 coiled about a supporting bar 69 extending within theframe vmember .springi is wound outwardly from a long .double IG. As isapparent from Fig. 7, the

leg portion iiD, the lbight v'Il of which is splayed so .as to exertpressure over a symmetrical area which reduces the probability ofeccentrically stressing the yoke. The respective spring ends l2, 13,reach forwardly and upwardly to engage the underside of top plate I. Itis obvious that s the spring 68 urges the yoke into clockwise rota- Thewide area of con-l tion, as viewed in Fig. 4. tact of the spring portionT0 with the dome 65 and the end thrust exerted on the yoke by the4overthrow springs 4 serves to take up the slight clearance at thepivots iiil and insure against possible sloppiness of operation at lowtemperatures.

To adjust the control temperature at which the thermostat is to operate,I provide an adjustment screw i4 operating within a threaded sleeve 'l5fixed rigidly at its .end to the bottom p0rtion i4 of the front framewall. Said bottom Aportion may be inclined from the vertical as requiredto cause the shaft screw 14 .to be substantially aligned with the shaft''l extending from the adjustment knob. In order to prevent the threadsl'on screw 14 from binding with those ythe screw shaft. These bearingsaccurately center the screw within the sleeve. The bias of .spring 68urges the bell crank leg 63 against the rounded end of the screw shaftand maintains the respective screw threads in surface contact. Thespacedbearings prevent wobbling of the screw shaft at low temperatureseven though-the bearv'ings may have liberal clearances. The function ofthe threaded portions becomes merely that of converting rotationalmovement into axial Imovementor "the-screw shaft, changing the vpositionof the yoke relative to the movable contacts according to the directionof rotation of the screw. In actual practice in a thermostat having acontrol range up to 1000 degrees F., the maximum contact displacement isabout of an inch. The maximum rise of the bimetal contact assembly 33relative to the xed contact assembly 35 at the floor of the yoke may beestablished by the adjustment screws 'i9 arranged on inwardly extendingportions of the yoke side walls, as is apparent in Figs. 3 and l0.ConsideringY the multiplication of movement ai'orded by the pivotedyoke, it will be apparent that the angular rotation of leg 63 is but asmall fraction of the contact displacement. This emphasizes the need forrigidity of the bell crank structure because any flexure of the legportion 63 would obviously disturb the calibration of the thermostat.

A. tongue Sil struck rearwardly from the frame wall acts a stop incooperation with a linger 8i carried by the screw shaft. A ball and pinarrangement 82 fixed to the end of the screw shaft is provided forcooperation with the universal joint coupling of the shaft T.

It is, of course, obvious that the position of the yoke contactsrelative to the movable contacts establishes the approximate controltemperature. The spring pivot screw 43 moving with the yoke andtherefore having a xed relation to the contact plane of the yoke contactpairs insures a uniform action of the snap spring 44 in eitherdirection. As is well known, spring 44 snaps or overthrows as the knifeedge 45 passes through the plane of the pivot screw tip. v

The thermostat may be used as an on-ofl switch by providing a stopmember which will support the bimetal strip contact assembly 33 out ofcontact with yoke contacts 35 when the yoke is operated to a positionrepresentative of a temperature below the lowest control temperature.For example, the instant embodiment provides control over a range offrom 250 degrees F. to above 900 degrees F. and. the yoke may be rotateddownwardly to a position representative of 100 degrees or less.Therefore, by restraining movement of the bimetal element so that itcannot follow the yoke to the lower extreme of movement, I can establisha position at which. the contacts 33 and 35 will not close regardless ofhow low the ambient temperature may go. This, of course, has been donein other thermostats, but insofar as `I am aware Without providing thefacility of adjustment and positive action provided herein.

As shown in Figs. fi and 9, l.' pivotally attach to the inner face of alframe side wall I2, a stop member having relatively large area,triangular, plate $3 in. surface contact with the frame wall and anextending arm portion 84 which reaches angularly outwardly and forwardlyfrom plate 83 to position a nose $35 in the central portion of thebimetal strip 2b at the forward extremity of the flexible portionthereof. It is understood, of course, that the stop plate and arm are ofsufficiently heavy stock to adequately resist the forces which may beexerted against it as the bimetal element responds to a low ambienttemperature condition. By reaching `forwardly to the outer extremity ofthe flexible portion of bimetal 2i), .it is apparent that the separationof the respective contacts will be maintained without undue strain onthe bimetal system or the stop member, for when bimetal 20 cools itdeects upwardly in opposition to the downward deflection of bimetal i8.

For adjustment of the stop member to the desired off-point temperature,there is provided an arcuate slot E6 in the frame wall whichaccommodates a pair of screws 8l which. enter tapped openings in plate83. Suitable lock washers 88 between the screw heads and the frame wallprovide means for securely holding the stop plate 83 againstdisplacement from a preset position. The large frictional area ofContact between the plate 83 and the frame wall contributes to thestability of the stop member. Rotation of dial 5, Fig. 2, to bring theoff-point marking of the dial in registry with index I brings the yoke36 to its Fig. 4 position, which is well below the lowest controltemperature. The contacts remain open regardless of the ambienttemperature to which the bimetal element is exposed, because the bimetalis restrained from reaching the yoke contacts in their off-pointposition.

A condition may frequently arise when the bimetal element will beexposed to the biasing effort of the spring li! when the bimetal is athigh temperature and most susceptible to damage. For example, if therange had been operating under a high temperature setting immediatelybefore being shut down by turning the thermostat to off position, thebimetal element would have the upward deflection characteristic of hightemperature, as suggested in Fig. 6. The retraction of adjustmentspindle 14 from leg 64 releases the yoke for rotation clockwise of Fig.6, and the yoke would so rotate until its adjustment screws l5 engagedthe upper element of contact assembly 33. This yoke movement would besufiicient to open the control circuit, but nevertheless the yoke wouldbe hung up on the bimetal, which would then be exposed to the bias ofthe spring. At elevated temperatures bimetal elements are structurallyweak and could be given a permanent, damaging set by an unduly heavyspring bias. I consider a suitable spring to be one which will enforcerotation of the yoke but under operative conditions in the upper zone ofthe temperature range of the thermostat will not stress the bimetalbeyond its elastic limit at said elevated temperature.

As the bimetal temperature drops and the element moves toward a concaveshape, the yoke drops also; so there is no possibility of an accidentalclosure of the control circuit. Eventually, the movement of the bimetalwill be interrupted by engagement with the nose G5. It will be notedthat under this latter condition, the stop niember supports the bimetalclosely adjacent the point at which the bias most effective, and thereis no danger that the bias will lose its calibration or take a permanentset due to spring bias, even though the thermostat may be in the offposition for a long period.

While there has been described what is at present considered to be thepreferred embodiment of the invention, it will be understood thatvarious modications may be made therein, and it is intended to cover inthe appended claims all such modifications as fall within the truespirit and scope of the invention.

I claim:

l. A thermostat of the bimetal type responsive to the temperature of abody heated by electrically controllable heating means, comprising framehaving a heat-conducting wall adapted to be secured to said body in heatexchange relation therewith, a heat-responsive element comprising a rstbimetal strip fixed at one end to and extending from said wall, and asecond bimetal strip fixed to and extending from the free end of said.first strip, said stripsy exingin opposition' in response totemperaturechangasaid secondI strip being stiffened at itsiouter portionto limit flexure to -a relatively small portion-'thereof adjacent saidfirst strip,` contact `means'sinsulatedly carried by said second stripadjacent the` free' end thereof, a yoke member pivotally..affixed` tothe frame and extending 'therefromvto encloseA said heat-responsiveelement, the planes cfmovement of said yoke member andsaid'heat-responsive element being co-incident,vsnap springmeansinterposed between said' yoke-and thexlree` end of said secondstrip,'contact/meanscarried by said yoke member forcooper-ation:fwithrsaidz first Contact means, -a bellcranl;-xed"to'--said yoke memberand havinga leg extending angularlytherefrom in the plane of rotation' of said member, a female-threadedsleeve fixed to`-saidH frame `andv extendingangularlyI with -respect tosaid bell crank leg, a Vmale-threadedyoke-adjustment spindle associatedwith saicl-sleeve for engagement with said bell crank leg, there beingsubstantial radialv clearance betweenL the -respec-` tive threads ofsaid sleeve and-said spindle in axial alignment within saidv sleeve,spring-means interposed between saidy frame and-saidyoke member toenforce rotation ofthe latter to bring the bell crank leg intoengagementwith said` spindle, whereby uponrotation'of said spindlein oneor another direction tlie'yokemeinberwill adjust the relative positionof the'respective contact means, a stop member fixed to said frame andengageable with the second bim-etal'strip to@ 'interrupt movement ofsaid bimetal'element ton ward said yoke member contacts-tov maintain an`open circuit position at a predetermined low insulator means floatinglyvcarriedbysaid terminal block supporting each said'flexible con--Y ductorto maintain the same in spaced relation ship one with the otherthroughout the fulll range of yoke member adjustment, andi meansaccesv3g), rotate relative to said heat-responsive element to sibleremote from the frame I`member toeffect-f rotation of said adjustmentspindle. Y

2. A high temperatureresponsive thermostat of the bimetal typecomprising a frame having a 'i heat-conducting wall,a heat-responsiveelement comprising a first bimetal strip fixed atvoneend to andextending from saidwall member and a second bimetal strip fixed toandextendingfrom the free end of said first strip, said strips flexingin opposition-in response to temperature change,

said second strip being stiffened at its outer portion to limit iiexureto a relatively small portion thereof vadjacent-said first strip,contact means.l

insulatedly carried by said second strip adjacent the free end thereof,a yoke member pivotallyaffixed to the frame and extending therefrom'tokenclose said heat-responsive element, the planes of movement of saidyoke member and said heatresponsive element being coincident, contactmeans carried by said yoke member for cooperation with said firstcontact means, a bell crank.

fixed to said yoke member and having a legex-` tending angularlytherefrom in the'plane of rotation of said member, afemale-threadedzsleeve.

fixed to said frame and extending angularly with respect to said bellcrank leg, a male-threaded yoke-adjustment spindlel associated withsaid` 10i sleeve for engagement withl said bell crank leg, there beingsubstantial radial clearance between the respective threads of saidsleeeve and said spindle, bearing. means for maintaining said spindle inaxial alignment within said sleeve, spring means interposed between saidframe and saidY yoke member toenforce rotation of the lattervtobringthebell crank leg into engagement with said spindle, whereby upon rotationof said spindle in one or another direction the yoke member will rotaterelative to said heat-responsive element toadjust Athe relative positionof the respective contact means, a terminal block fixed to said frame,electric-terminal means lrelatively loosely disposed in said block andcorresponding in number with said yoke member contact means,flexible-conductors interconnecting said contact means-and said terminalmeans, insulator means oatingly carried by said terminal blocksupporting each said flexible conductor to maintain the same in spacedrelationship one with the other throughout the full range of yoke memberadjustment, and means accessible remote from the frame member to effectrotation of said adjustment spindle.

3. A high temperature responsive thermostat of the bimetal type having aframe, a bimetal element fixed at one end to said frame andextending'therefrom, contact means insulatedly carried by said bimetalelement adjacent the free end thereof, a yoke pivotally affixed to saidframe and extending therefrom parallel to said bimetal element, contactmeans carried by said yoke for .eooperation with said rst contact means,and temperature adjustmentvmeans comprising a rigid leg member extendingangularly from said yoke in the-plane of rotation thereof, afemale-threaded sleeve xedto vsaid frameand extending outwardly-fromsaid leg member in theplane of rotation thereof, a cooperativelymale-threaded adjustment spindle disposed within said sleeve inalignment with said leg member, there being a substantial radialclearance between the respective threads of said sleeve and spindle,bearing -lmeans for maintaining thefco-axial relation of said spindleand saidA sleeve, and spring means exerting pressure on said yoke over arelatively wide contact area symmetrical thereof to rotate the yoke tomaintain said leg member in pressure engagement with said spindlewhereby said spindle is axially displaced within said sleeve to maintainthe'respective screw threads in facial contact.

4. A highV temperature responsive thermostat of the bimetal typecomprising a frame, a bimetal element fixed at one end to said frame andextending therefrom, contact means insulatedly carried by saidbimetal'element adjacent the free end thereof, a yoke pivotally aflixedto said frame and extending therefrom parallel tosaid bimetal element',contact means carried by said yoke for cooperation with said firstcontact means, spring means interposed between said yoke and saidbimetal element, temperature adjustment means comprising a rigid legmember extending angularly from said yoke in the plane of rotationthereof, a female-threaded sleeve fixed to saidA frame` and extendingoutwardly from said leg member in the plane of rotation thereof, acooperatively male threaded adjustment spindle disposed withinsaidsleeve in alignment with said leg member, there being a substantialradial f clearance between the respective threads of said sleeveandspindle, bearing: means for niaintain- A ing the co-axial relationofsaid spindle and said sleeve, spring means exerting pressure on saidyoke to rotate the yoke to maintain said leg member in pressureengagement with said spindle whereby said yoke will rotate relative tosaid frame in a direction according to the direction of rotation of saidspindle, and a rigid member fixed to said frame and engageable with saidbimetal element adjacent the contact means there of to preventengagement of the respective contact means when said yoke is rotated inone direction to a predetermined position.

5. A high temperature responsive thermostat ci the bimetal typecomprising a frame, a bimetal element fixed at one end to said frame andextending therefrom, contact means insulatedly carried by said bimetalelement adjacent the free end thereof, a yoke pivotally affixed to saidframe and extending therefrom parallel to said bimetal element, contactmeans carried by said yoke for cooperation with said first contactmeans, spring means interposed between said yok-e and said bimetalelement, temperature adjustment means comprising a rigid leg memberextending angularly from said yoke in the piane oi rotation thereof, afemale-threaded sleeve fixed to said frame and extending outwardly fromsaid leg member in the plane of rotation thereof, a cooperativelymale-threaded adjustment spindle disposed within said sleeve inalignment with said leg member, bearing means for maintaining theco-axial relation of said spindle and said sleeve, spring means torotate the yoke to maintain said leg member in pressure engagement withsaid spindle whereby said yoke will rotate relative to said frame in adirection according to the direction of rotation of said spindle, and arigid member adjustably fixed to said frame and engageable with thebimetal element adjacent the contact means thereof to prevent engagementof the respective contact means when said yoke is rotated in onedirectionto a predetermined position,

6. A high temperature thermostat of the bimetal type comprising a frame,a temperatureresponsive bimetal element carried thereby, a yokepivotally mounted on said frame for movement relative to said'temperature-responsive element, contact means respectively carried bysaid temperature-responsive element and said yoke, a terminal block ofinsulation material fixed to said frame, terminal means disposed withinsaid terminal block, there being substantial clearance between saidterminal means and said block, flexible conductors between said yokecontact means and said terminal means, insulation means freely slidablewithin said terminal block and engaging said conductors to support thesame intermediate said yoke and said terminal block, and means forrotating said yoke relative to said frame comprising a threaded member'xed to said frame, a cooperatively threaded member fixed to said frame,a cooperatively threaded member coaxially associated therewith forengagement with said yoke member, there being substantial radialclearance between the respective threads, means for maintaining saidthreaded elements in coaxial relationship, and spring means displacingone of said threaded elements axially with respect to the other tomaintain the threads thereof in surface contact.

7 A high temperature thermostat comprising a frame, atemperature-responsive element carried thereby, a yoke pivotally mountedon said frame for movement relative to said temperatureresponsiveelement, Contact means respectively carried by saidtemperature-responsive element and said yoke, a terminal block ofinsulation material fixed to said frame, said block having polygonalapertures therein, terminal means disposed within said terminal blockapertures, said terminal means having a polygonal cross section similarto that of said apertures and there being substantial clearance betweenthe respective walls of said terminal means and said block apertures,flexible conductors between said yoke contact means and said terminalmeans, insulation means slidably supported by said terminal block andengaging said conductors to support the same intermediate said yoke andsaid terminal block, and means for rotating said yoke relative to saidframe for adjusting the position of the respective contacts relative toeach other.

8. In a high temperature responsive thermostat of the bimetal typehaving a frame, a bimetal element fixed at one end to said frame andextending therefrom, contact means insulatedly carried by said bimetalelement adjacent the free end thereof, a yoke pivotally affixed to saidframe and extending therefrom parallel to said bimetal element, contactmeans carried by said yoke for cooperation with said first contactmeans, and spring means interposed between said yoke and said bimetalelement: temperature adjustment means comprising a rigid leg memberextending` angularly from said yoke in the plane of rotation thereof, afemale-threaded sleeve fixed to said frame and extending angularly withrespect to said leg member, a cooperatively male-threaded adjustmentspindle disposed within said sleeve in alignment with said leg member,there being a substantial radial clearance between the respectivethreads of said sleeve and spindle, bearing means for maintaining theco-axial relation of said spindle and said sleeve, and spring meansexerting pressure on said yoke over a relatively wide contact areasymmetrical thereof to rotate the yoke to maintainsaid leg member inpressure engagement with said spindle whereby said spindle is axiallydisplaced within said sleeve to maintain the respective screw threads infacial contact.

9. In a high temperature responsive thermostat of the bimetal typeincluding a frame having a heat-conducting wall, a bimetal member fixedat one end to and extending from said wall member, contact meansinsulatedly carried by said bimetal member adjacent the free endthereof, a yoke member pivotally affixed to the frame and extendingtherefrom to enclose said heat-responsive element, the planes ofmovement of said yoke member and said bimetal member being coincident,and contact means carried by said yoke member for cooperation with saidrst Contact means; temperature-adjustment means comprising a bell crankiixed to said yoke member and having a leg extending angularly therefromin the plane of rotation of said member, a female-threaded sleeve xed tosaid frame and extending angularly with respect to said bell crank leg,a male-threaded yoke-adjustment spindle associated with said sleeve forengagement with said bell crank leg, there being substantial radialclearance between the respective threads of said sleeve and saidspindle, bearing means for maintaining said spindle co-axial withrespect to said sleeve, spring means interposed between said frame andsaid yoke member to enforce rotation of the latter to bring the bellcrank leg into engagement with said spindle and urge adjacent faces ofthe respective threads into contact whereby upon rotation of saidspindle in one or another direction the yoke member will rotate relativeto said heatresponsive element to adjust the relative position of therespective contact means, and means accessible remote from said framefor rotating said adjustment spindle.

10. A bimetallic thermostat comprising a frame, a thermo-sensitivebimetal system having a predetermined temperature range of operation,said system including a bimetal element xed at one end to the frame andextending therefrom in cantilever fashion and contact means carried bysaid element near the free end thereof, a yoke structure pivotallymounted in said frame andextending parallel to said bimetal element forrotation in the plane of action thereof, contact'means carried by saidyoke structure for cooperation with said first-named contact means,stopmeans xed to said yoke and engageable with an element of saidbirnetal system to limit relative movement therebetween, spring meansinterposed between said yoke and said frame and biasing said yoke intorotation in a` direction which engages said stop means with said bimetalsystem, and adjustment screw means carried by said frame remote fromsaid spring means, said screw means being effective upon rotation in onedirection to rotate said yoke structure in a direction opposing saidspring bias, and withdrawing from said yoke structure upon rotation inthe opposite direction, whereby the maximum effort which the springmeans is capable of exerting on said bimetal system upon contact of saidstop means with said element thereof is independent of the extentpofwithdrawal of said adjustment screw means from said yoke structure,

11. A bimetal thermostat as in claim 10, including a rigid stop memberextending from said frame to a point adjacent the points of engagementof said stop means with said bimetal system element but on the oppositeside thereof, whereby to limit the extent of rotation of said yokestructure induced by said spring means.

NICHOLAS MILLER.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 2,061,419 Ettinger et al. Nov. 17, 1936 2,194,999 Clark Mar.26, 1940 2,258,258 Mikeska Oct. '7, 1941

